Editing DDR2 SDRAM (section)

=== Chips and modules ===
For use in computers, DDR2 SDRAM is supplied in [[DIMM]]s with 240 pins and a single locating notch. Laptop DDR2 [[SO-DIMM]]s have 200 pins and often come identified by an additional '''S''' in their designation. DIMMs are identified by their peak transfer capacity (often called bandwidth).

{| class="wikitable sortable"
|+ Comparison of DDR2 SDRAM standards

! colspan="3" scope="col" | Name
! colspan="2" scope="col" | [[Chip (computing)|Chip]]
! colspan="3" scope="col" | [[Bus (computing)|Bus]]
! colspan="2" scope="col" | [[Memory timings|Timings]]

|-
! scope="col" | Standard
! scope="col" | Type
! scope="col" | Module
! scope="col" |[[Clock rate]] {{Small|([[MHz]])}}
! scope="col" | Cycle time {{Small|([[Nanosecond|ns]])}}<ref>Cycle time is the inverse of the I/O bus clock frequency; e.g., 1/(100&nbsp;MHz) = 10&nbsp;ns per clock cycle.</ref>
! scope="col" | Clock rate {{Small|(MHz)}}
! scope="col" | [[Transfer (computing)|Transfer rate]] {{Small|(MT/s)}}
! scope="col" | [[Bandwidth (computing)|Bandwidth]] <small>([[MB/s]])</small>
! scope="col" | CL-T{{Sub|RCD}}-T{{Sub|RP}}<ref>{{cite journal |date=April 2008 |title=DDR2 SDRAM SPECIFICATION |version=JESD79-2E |publisher=[[JEDEC]] |pages=78 |url=http://www.jedec.org/download/search/JESD79-2E.pdf |access-date=2009-03-14 }}</ref><ref>{{cite journal |date=November 2007 |title=SPECIALITY DDR2-1066 SDRAM |publisher=[[JEDEC]] |pages=70 |url=http://www.jedec.org/download/search/JESD208.pdf |access-date=2009-03-14 }}</ref>
! scope="col" | [[CAS latency]] {{Small|(ns)}}

|-
! rowspan="2" scope="row" | DDR2-400
| scope="row" | B
| rowspan="2" | PC2-3200
| rowspan="2" | 100
| rowspan="2" | 10
| rowspan="2" | 200
| rowspan="2" | 400
| rowspan="2" | 3200
| 3-3-3
| 15

|-
| scope="row" | C
| 4-4-4
| 20

|-
! rowspan="2" scope="row" | DDR2-533
| scope="row" | B
| rowspan="2" | PC2-4200*
| rowspan="2" | 133
| rowspan="2" | 7.5
| rowspan="2" | 266
| rowspan="2" | 533
| rowspan="2" | 4266
| 3-3-3
| 11.25

|-
| scope="row" | C
| 4-4-4
| 12

|-
! rowspan="2" scope="row" | DDR2-667
| scope="row" | C
| rowspan="2" | PC2-5300*
| rowspan="2" | 166
| rowspan="2" | 6 
| rowspan="2" | 333
| rowspan="2" | 667
| rowspan="2" | 5333
| 4-4-4
| 12

|-
| scope="row" | D
| 5-5-5
| 12 or 15

|-
! rowspan="3" scope="row" | DDR2-800
| scope="row" | C
| rowspan="3" | PC2-6400
| rowspan="3" | 200
| rowspan="3" | 5
| rowspan="3" | 400
| rowspan="3" | 800
| rowspan="3" | 6400
| 4-4-4 
| 10

|-
| scope="row" | D
| 5-5-5
| 12.5

|-
| scope="row" | E
| 6-6-6
| 12 or 15

|-
! rowspan="3" scope="row" | DDR2-1066
| scope="row" | D
| rowspan="3" | PC2-8500*
| rowspan="3" | 266
| rowspan="3" | 3.75
| rowspan="3" | 533
| rowspan="3" | 1066
| rowspan="3" | 8533
| 5-5-5
| 9.375

|-
| scope="row" | E
| 6-6-6
| 11.25

|-
| scope="row" | F
| 7-7-7
| 13.125
|}

{|class="wikitable floatright" style="text-align:center;"
|+ Relative speed comparison between similar modules
! rowspan="2" |
! colspan="2" | PC-5300
! colspan="3" | PC-6400
|-
! 5-5-5
! 4-4-4
! 6-6-6
! 5-5-5
! 4-4-4
|-
|| PC2-3200 4-4-4 || % || % || +33% || +60% || % 
|-
|| PC2-3200 3-3-3 || % || % || = || +20% || % 
|-
|| PC2-4200 4-4-4 || % || % || = || +21% || % 
|-
|| PC2-4200 3-3-3 || % || % || −24% || −9% || % 
|-
|| PC2-5300 5-5-5 || % || % || = || +21% || %
|-
|| PC2-5300 4-4-4 || % || % || −19% || −3% || % 
|-
|| PC2-6400 6-6-6 || % || % || = || +20% || % 
|-
|| PC2-6400 5-5-5 || % || % || −16% || = || % 
|-
|| PC2-6400 4-4-4 || % || % || −33% || −20% || % 
|-
|| PC2-8500 7-7-7 || % || % || −12% || +6% || % 
|-
|| PC2-8500 6-6-6 || % || % || −25% || −9% || % 
|-
|| PC2-8500 5-5-5 || % || % || −37% || −24% || % 
|}
<nowiki>*</nowiki> ''Some manufacturers label their DDR2 modules as PC2-4300, PC2-5400 or PC2-8600 instead of the respective names suggested by JEDEC. At least one manufacturer has reported this reflects successful testing at a higher-than-standard data rate<ref>[http://www.metku.net/index.html?path=reviews/ddr2_1/index_eng Mushkin PC2-5300 vs. Corsair PC2-5400]</ref> whilst others simply round up for the name.''

'''Note:''' DDR2-xxx denotes data transfer rate, and describes raw DDR chips, whereas PC2-xxxx denotes theoretical bandwidth (with the last two digits truncated), and is used to describe assembled DIMMs. Bandwidth is calculated by taking transfers per second and multiplying by eight. This is because DDR2 memory modules transfer data on a bus that is 64 data bits wide, and since a byte comprises 8 bits, this equates to 8 bytes of data per transfer.

[[File:DDR2 F 'Fully Buffer' vs 'Parity' notch position.jpg|alt=DDR2 P vs F Server DIMM's Notch Positions compared|thumb|left|DDR2 '''P''' vs '''F''' ''Server'' DIMM's Notch Positions compared]]
In addition to bandwidth and capacity variants, modules can:

# Optionally implement [[ECC memory|ECC]], which is an extra data byte lane used for correcting minor errors and detecting major errors for better reliability. Modules with ECC are identified by an additional ECC in their designation. PC2-4200&nbsp;ECC is a PC2-4200 module with ECC. An additional ''P'' can be added at the end of the designation, P standing for parity (ex : PC2-5300P).
# [[File:Intel ® 6402 Advanced Memory Buffer..jpg|alt=Intel ® 6402 Advanced Memory Buffer|thumb|Intel ® 6402 Advanced Memory Buffer]]Be "registered" ("buffered"), which improves signal integrity (and hence potentially clock rates and physical slot capacity) by electrically buffering the signals at a cost of an extra clock of increased latency. Those modules are identified by an additional '''R''' in their designation, whereas non-registered (a.k.a. "[[Unbuffered memory|unbuffered]]") RAM ''may be'' identified by an additional '''U''' in the designation.  PC2-4200R is a registered PC2-4200 module, PC2-4200R&nbsp;ECC is the same module but with additional ECC. 
# Be aware [[Fully Buffered DIMM|fully buffered]] modules, which are designated by '''F''' or '''FB''' do not have the same notch position as other classes. Fully buffered modules cannot be used with motherboards that are made for registered modules, and the different notch position physically prevents their insertion.

'''Note:''' 
* Registered and un-buffered SDRAM generally cannot be mixed on the same channel.
* The highest-rated DDR2 modules in 2009 operate at 533&nbsp;MHz (1066&nbsp;MT/s), compared to the highest-rated DDR modules operating at 200&nbsp;MHz (400&nbsp;MT/s). At the same time, the CAS latency of 11.2&nbsp;ns = 6&nbsp;/&nbsp;(bus&nbsp;clock&nbsp;rate) for the best PC2-8500 modules is comparable to that of 10&nbsp;ns = 4&nbsp;/&nbsp;(bus&nbsp;clock&nbsp;rate) for the best PC-3200 modules.